1. Field Of The Invention
The present invention relates to a process for the manufacture of molded articles out of injection molding material in which the molded articles are separated from the mold with the aid of air and/or inert gas. The process is especially suitable for the manufacture of injection molded parts out of fluid silicone rubber.
2. Background Information
The manufacture of injection molded articles is an often used method for manufacturing molded articles. Examples of suitable materials capable of being injection molded include polyethylene, polypropylene, polycarbonate, PVC, poIyslyrol, ABS, poIyacelale HDPE, polyterephthalale, poIyamide and silicone rubber (c.f., e.g., Hans Gastrow, "Der Spritz-giess Werkzeugbau", Hanser-Verlag 1982).
Recently this technology has also been employed in the manufacture of molded articles out of silicone rubber.
The careful automatic extraction of molded articles to be produced represents a problem in injection molding technology.
It is known that in the extraction of flat or humped molded articles usually out of the female mold or out of the core ejection pads or rods for lifting the finished part out of the mold in order to enable subsequent ejection can be used. This state of the art, however, has a significant disadvantage in that is known that rubber, especially silicone rubber, has a very low initial tearing resistance and a very low resistance to tear propagation under the usual deformation conditions in the high temperatures of up to 250.degree. C. prevailing in the mold, thus it is almost unavoidable that the finished parts are teared and/or punctured by the exiting rods and thereby causing damage. Cooling down of the mold after vulcanization for the purpose of careful removal from the mold is not practicable for economic reasons.
In other practiced processes for removal from the mold, compressed air is sometimes additionally blown in across the exiting rods and their slaving, in order to support the removal from (he molds. This process, however, has additional latent problems, namely during the injection process, the returned ejector rods ought to be locked-off tight with the slaving against non-vulcanized rubber flowing in, in order to prevent spraying (flash), which otherwise results in expensive subsequent processing of the parts; for non-vulcanized rubber, especially silicone rubber, such rubber reaches an extremely low viscosity at high temperatures and especially under great shearing stress and can easily flow under pressure into all kinds of parting planes and gaps. However, as the mold must be run al temperatures up to 250.degree. C., under these conditions the parts must remain easily practicable, an unsatisfactory compromise must usually be reached here. In addition, in working with parts used in this manner, it turns out that the rubbers to be processed in this regard have an enormous abrasive effect and quickly bring about wear and thus an increase of clearance in the slaving.
Such constructions therefore enable, at best a short-term satisfactory running of the installation.